Neb. Rev. Stat. § 18-2311

All original and renewal certificates shall be good for one year from their dates, but any certificate may be revoked by the air conditioning air distribution board at any time after a hearing upon sufficient notice after sworn charges are filed with the board showing the holder of the certificate to be then incompetent, guilty of willful breach of the rules, regulations, or requirements of the board or of the laws or ordinances relating thereto, or of other causes sufficient for the revocation of the certificate as determined by the city council or village board of trustees of which charges and hearing the holder of such certificate shall have written notice.